- amplitude
- extent of the displacement caused by a wave

- atomic orbital
- mathematical function that describes the behavior of an electron in an atom (also called the wavefunction)

- Aufbau principle
- procedure in which the electron configuration of the elements is determined by “building” them in order of atomic numbers, adding one proton to the nucleus and one electron to the proper subshell at a time

- blackbody
- idealized perfect absorber of all incident electromagnetic radiation; such bodies emit electromagnetic radiation in characteristic continuous spectra called blackbody radiation

- Bohr’s model of the hydrogen atom
- structural model in which an electron moves around the nucleus only in circular orbits, each with a specific allowed radius

- continuous spectrum
- electromagnetic radiation given off in an unbroken series of wavelengths (e.g., white light from the sun)

- core electron
- electron in an atom that occupies the orbitals of the inner shells

- covalent radius
- one-half the distance between the nuclei of two identical atoms when they are joined by a covalent bond

*d*orbital- region of space with high electron density that is either four lobed or contains a dumbbell and torus shape; describes orbitals with
*l*= 2.

- degenerate orbitals
- orbitals that have the same energy

- effective nuclear charge
- charge that leads to the Coulomb force exerted by the nucleus on an electron, calculated as the nuclear charge minus shielding

- electromagnetic radiation
- energy transmitted by waves that have an electric-field component and a magnetic-field component

- electromagnetic spectrum
- range of energies that electromagnetic radiation can comprise, including radio, microwaves, infrared, visible, ultraviolet, X-rays, and gamma rays

- electron affinity
- energy change associated with addition of an electron to a gaseous atom or ion

- electron configuration
- listing that identifies the electron occupancy of an atom’s shells and subshells

- electron density
- a measure of the probability of locating an electron in a particular region of space, it is equal to the squared absolute value of the wave function
*ψ*

- excited state
- state having an energy greater than the ground-state energy

*f*orbital- multilobed region of space with high electron density, describes orbitals with
*l*= 3

- frequency (
*ν*) - number of wave cycles (peaks or troughs) that pass a specified point in space per unit time

- ground state
- state in which the electrons in an atom, ion, or molecule have the lowest energy possible

- Heisenberg uncertainty principle
- rule stating that it is impossible to exactly determine both certain conjugate dynamical properties such as the momentum and the position of a particle at the same time. The uncertainty principle is a consequence of quantum particles exhibiting wave–particle duality

- hertz (Hz)
- the unit of frequency, which is the number of cycles per second, s
^{−1}

- Hund’s rule
- every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin

- intensity
- property of wave-propagated energy related to the amplitude of the wave, such as brightness of light or loudness of sound

- interference pattern
- pattern typically consisting of alternating bright and dark fringes; it results from constructive and destructive interference of waves

- ionization energy
- energy required to remove an electron from a gaseous atom or ion

- isoelectronic
- group of ions or atoms that have identical electron configurations

- line spectrum
- electromagnetic radiation emitted at discrete wavelengths by a specific atom (or atoms) in an excited state

- magnetic quantum number (
*m*)_{l} - quantum number signifying the orientation of an atomic orbital around the nucleus

- node
- any point of a standing wave with zero amplitude

- orbital diagram
- pictorial representation of the electron configuration showing each orbital as a box and each electron as an arrow

*p*orbital- dumbbell-shaped region of space with high electron density, describes orbitals with
*l*= 1

- Pauli exclusion principle
- specifies that no two electrons in an atom can have the same value for all four quantum numbers

- photon
- smallest possible packet of electromagnetic radiation, a particle of light

- principal quantum number (
*n*) - quantum number specifying the shell an electron occupies in an atom

- quantization
- limitation of some property to specific discrete values, not continuous

- quantum mechanics
- field of study that includes quantization of energy, wave-particle duality, and the Heisenberg uncertainty principle to describe matter

- quantum number
- number having only specific allowed values and used to characterize the arrangement of electrons in an atom

*s*orbital- spherical region of space with high electron density, describes orbitals with
*l*= 0

- secondary (angular momentum) quantum number (
*l*) - quantum number distinguishing the different shapes of orbitals; it is also a measure of the orbital angular momentum

- shell
- atomic orbitals with the same principal quantum number,
*n*

- spin quantum number (
*m*)_{s} - number specifying the electron spin direction, either $+\phantom{\rule{0.2em}{0ex}}\frac{1}{2}$ or $-\phantom{\rule{0.2em}{0ex}}\frac{1}{2}$

- standing wave
- (also, stationary wave) localized wave phenomenon characterized by discrete wavelengths determined by the boundary conditions used to generate the waves; standing waves are inherently quantized

- subshell
- atomic orbitals with the same values of
*n*and*l*

- valence electrons
- electrons in the outermost or valence shell (highest value of
*n*) of a ground-state atom

- valence shell
- outermost shell of electrons in a ground-state atom

- wave
- oscillation of a property over time or space; can transport energy from one point to another

- wave-particle duality
- observation that elementary particles can exhibit both wave-like and particle-like properties

- wavefunction (
*ψ*) - mathematical description of an atomic orbital that describes the shape of the orbital; it can be used to calculate the probability of finding the electron at any given location in the orbital, as well as dynamical variables such as the energy and the angular momentum

- wavelength (
*λ*) - distance between two consecutive peaks or troughs in a wave